Centralized traffic controlling system for railroads



w, D. HAlLEs 2,097,789

CENTRALIZED TRAFFIC CONTROLLING SYSTEM FOR RAILROADS Npv. 2, 1937.

6 Sheets-Sheet lV Filed July 30, 1935 Iv N: J H R am Tm mw A A... r m,jm flwlwl v Vf 3 1 To Aromm* ..lllJrl E, @F. P IWW lllww @n lvT s# Nk H+V E im om S ma E I .1+ I ..Al+ l rl.m www l. mm mm Law HARM 3 T omv k|3 uz d@ I W. D. HAILES Nov. 2, 1937.

CENTRALIZ'ED TRAFFIC CONTROLLING SYSTEM FOR RAILROADS Filed July 50,1955 6 Sheets-Sheet 2 MNZTMZ@ BY w ATTQRN EY W. D. HAILES Nov. 2, 1937.

VCENTRALIZED TRAFFIC CONTROLLING SYSTEM FQR RAILOADS 6 Sheets-Sheet 5Filed July 30, 1935 Nov. 2, 1937. W. D. HAILES CENTRALIZED TRAFFICCONTROLLING SYSTEM FOR RAILROADS 6 Sheets-Sheet 4 Filed July 50, 1935 JEM Mum @ ATTORNEY 6 Sheets-Sheet 5 ATTORN EY W. D. HAlLES CENTEALIZEDTRAFFIC CONTROLLING SYSTEM FOR RAILROADS Filed July 50, 1935 No'v. z,1937.

Nov. 2, 1937.

w. D. HAILES Filed July 50, 1935 S EN Patented Nov. 2, 1937 UNITEDSTATES PATENT OFFICE wiiiiam D. Hanes, Brighmmiv. Y.,y assignor toGeneral Railway` Signal` Company, Rochester,

Y Application July 30, 1935, Serial No. 33,8261

iol claims. (ci. 1ra-.iriaA This invention relates.V to centralizedtraffic controlling system; for railroads, and*` it more particularly.pertains to the communication part of such system.

By means of `thecentralized traffic controlling system. contemplated bythe present invention a central control olce is placed in communicationwith a number of outlying iieldstations in such a waythat: controls maybe transmitted to these field stations for governing the operation oftraflic controlling devices located at the various stations. Likewisethe conditions of the various traffic controlling devices at eachstationare transmitted from the station to the-control office to advise thevoperator of the location of trains and the condition of the trafficcontrolling devices, such conditions being transmitted as indications. Y

` `The present invention more particularly relates to a centralizedtraffic controlling system wherein the supervision of the trafcgoverning devices andthe indication of their conditions are accomplishedover a communication system comprising two line circuits, namely acontrol line circuit and an indication line circuit. The presentinvention is more particularly directed to a traffic controlling systemin which the distance between certain of the field stations and thecontrol oflce is such that it is impractical to transmit impulsesbetween the control oflice and these certain field stations without theuse of undesirably high line voltages or unduly large line conductors,`because of the length of the line circuits. f

An important feature of the present invention is a storage and repeaterarrangementwhereby it is'possible to operate one or more laterals orbranches extending from the main line of the communication system,without the necessity of looping the line circuit of such laterals inseries with the main line circuit, with the consequent need of high linevoltage and/or large line conductors. It will be obvious from thedescription which follows that a storage and repeater arrangement asdisclosed'in the present invention may be installed at the locationswhere such laterals branch off from the main line, thus repeatingcontrols and/or indications from the main line to these branches `with aconsequent reduction in line voltage and/or line conductor valuesrequired. It `will also be obvious that sub laterals may be branched oirthe above mentioned laterals by means of the storage and repeaterarrangement disclosed, all 'within' the 'scope of the present invention.

' Another'objectof the present invention is theY provision of arepeatingcircuit arrangement so that distant field stations may operateinconnection with the i,communication vsystem without the need ofincreasing-the size of the line conductors or providingv line voltagesbeyond a reasonable value. As a result of the repeating arrangementprovided in the present invention, installation costscf a centralizedtraffic controlling system are reduced because it is possible to keepthe'size of the line battery and the line conductors down to a.-mim'mum. In other words the present circuit arrangement yis so arrangedthat when the economical'limit of line wire size is reached and the`economical limit of line battery size is reached, 'the line circuitwill be arranged to repeat into another'line circuit and this processcan be repeated as often as required. This applies to the 'controllinecircuit and the indication line circuit.

Another object ofthe presentr invention is the provision of a circuitarrangement for directly repeating impulses from a primary control linecircuit which extends from the control oflice to a repeater location,into a secondary control line circuit whichv extends from the repeaterstation to one or more distant field stations.

Another object of the present invention is the provision of astoragearrangement at the repeater location, whereby indications transmittedfrom a distant eld station during one cycle of operation of thecommunication system are received and stored at theA repeater' locationand then retransmitted from the repeater location to the control ofliceduring a succeeding cycle of operations of the communication system.

Still another-objectofthe present invention is the provision of meansfor precharging the indication line circuitlextending from the controloiiice to the repeater location in advance of the transmission of Veachindication to the control office and for'precharging the indication linecircuit which extends from the repeater location to the distant fieldstations in advance of the transmission of each indication to therepeater station.

The advantages of Vsuch a precharging arrangement will be brieflypointed out during the following description, while a more detaileddiscussion of such an arrangement is set forth in applicants priorPatent No. 2,045,908, granted June 30, 1936.

Other objects, purposes and characteristic features of the presentinvention will be in part obvious from the accompanying drawings and inment at the control oice end of the communication system.

Figs. 2A, 2B and 2Cv illustrate in a diagrammatic and conventionalmanner'the circuit' organization at the repeater location.

Fig. 3V illustrates in a diagrammatic and conventional manner theapplication of the present invention to a eld station operating inconnection with the communication system.

In following the circuits of the present drawings Fig. 1B should beplaced below Fig. 1A, Fig. 2A shouldbe placed to-the right of Fig. 1A,Fig. 3 should be placed to the right of Fig. 2A, Fig. 2B should beplaced belowFig. 2A and Fig. 2C should be placed below Fig. 2B, with correspondingly identied lines in alignment.

, For-the purpose of simplifying the illustrations and facilitating inthe explanation the various parts and circuits constituting theembodiment of the invention have been shown diagrammatically and certainconventional illustrations have been employed, the drawings having beenmade more with the purpose of making it easier to understand theprocesses and mode of operation thanwith the idea of illustrating thespecic construction and 'arrangement of parts that would be employed inpractice. Thus the various relays and their contacts are illustrated ina conventional manner and symbols are used to indicate connectionsv tothe terminals ofY batteries or other sources of electric current insteadof showing all'of the wiring connections to these terminals. i l l Thesymbols and are employed to indicate the positive and negative terminalsrespectively of suitable batteries or other sources of current Yandthe-circuits with which these symbols are used always have currentflowing i-n the same direction, that is from Ato The symbols (B+) and (Bare employed to indicate the positiverand negative-terminalsrespectively of a battery or other source of direct current having amid-tap (CN) and the circuits with which these symbols are used Vmayhave current Viowing in one direction or another depending upon whetherthe circuitis connected to (B+) or (B ,Y A

Insome of the drawings, Figs. 2A, 2B and 2C for examplefcertain relayshave been shownrin full lines onrone drawing and inp-,dottedlines on anadjacent drawing. vThe relays shown in dotted lines have been given thesamereference characters as applied to these relays shownk in full linessince they are the same relays` as indicated by the dotted lineconnections from one drawing to another. It is thus believed unnecessaryto show the windings of the relays-illus- Y trated in dotted lines sincethe windings of these relays are indicated in the gures which showtherrelays by full lines. Y

Control oce equipment-The control oiice equipment includes a neutralline relay F'which repeats the impulses applied to the control linecircuit, comprising control line conductorv CL and control returnconductor CR, by means of battery -CB, l\Teutral line repeating relay FPYre- 'Bushnell Ser. No. 640,062 iled Oct.

peats the impulsesrapplied to relay F and since relay FP is of the quickacting type it follows the operations of relay F with small delay.Neutral line repeating relay ZFP repeats the operations of relay FP.Slow acting relay SA is used for defining the bounds of each operatingcycle, this relay being picked up* at the beginning of eachcycle,'remains up throughout the impulses during .the cycle Vand isdropped atthe end of the cycle.

Cycle determining relay C and code determining relay CD are picked up atthe beginning of ya cycle, during which controls are transmitted, Y bymeans of starting button SB. The detailed circuits for controlling theoperation of relays C and CD are not shown since they are immaterial foran understanding of the present invention and may be arranged as shownin detail in the prior application of T. J. Judge and C. S. 28, 1932,corresponding to British Patent No. 419,399.

f Field cycle determining relay FC remains down during a control cyclebut is picked up during a duplex cycle or a cycle for the transmissionof indications alone. The circuit arrangement of relay FC is likewiseomitted from the present drawing for the sake of simplicity and thisrelay may have its circuit controlled in the same manner as disclosed inthe above mentioned application Ser. No. 640,062.

Code sending relays PC and NC are for the purpose of providing (-1-) andimpulses respectively in the control line circuit during a cycle ofoperations. Relays MB and MF are for the purpose of receivingindications over the primary indication line circuit, comprisingindication line conductor IL and indication return conductor IR, duringan operating cycle. The executing circuit arrangement of relays MB andMF is not shown since this arrangement is immaterial for anunderstanding of the operation of the present embodiment and may beexactly the same as disclosed in the above mentioned prior applicationNo. 640,062. This executing circuit arrangement is controlled by thelower contacts on relays MB, MF, FP andFC as shown in Fig. 1B, with theindication storing relays being omitted. It will be understood that theindication storing relays are selectively energized with or current asdetermined by the positions of relays MB and with these relays selectedby the stepping relay bank as fully disclosed in the above mentionedapplication Ser. No. 640,062.

A suitable step-by-step relay bank is employed including relays VP, lV,2V and.' LV. Relays lV, 2V and LV take their steps during thecie-energized or oi periods of the controlline circuit and relay VPshifts its position during the energized or on periods of the controlline circuit.A When the stepping relays are picked up they are stuck upuntil the end of the cycle. Half-step relay VP is picked up and droppedduring alternate on'periods of the cycle, all-of which will be pointedout in detail. Control line impulsing relay E controls the applicationof impulses to the control line circuit by openingand closing theenergizing circuit of the PC and NC relays at the proper times asdetermined by the response of the stepping relay bank in the controloice to the impulses and the time spaces.

Resistance lCRS is acharging resistance for charging the indication linecircuit extending from the cnice to the repeater station to apply a flowof charging current at the beginning of Although not shown in thepresent drawings it will be understood that the control ocelis providedwith. a suitable control machine which includes a miniature trackdiagram representa` tive of the actual track layout in the eld. Cer`tain control levers and buttons which are manually operable to obtainthe desired control are included in the control machine, switch machinelever` SML and starting button SB being typical of such devices. It Willbe understood thata starting button is provided for each `group ofcontrol levers and is associated'with a particular eld station so thatthe positioning of the con-v trol levers for a particular stationresults inthe transmission of controls to that station follow# ing theoperation of the associated starting button. Station selection isprovided by the particular CD relay which isv picked up in response tothe operation of a particular starting button, by connecting the PC andNC relays to the channel circuits selected by the stepping relay bank bymeans or code jumpers connected in various combinations for providing astation selecting code.

Repeater station equipment- Referring to Figs. 2A, 2B and 2C therepeater station includes a biased to neutral polar kline relay F1 whichrepeats the polar impulses applied to the primary control line circuitin the control oiice. The and impulses applied to the primary controlline circuit and received by relay F1 eitiect the operation of relays`FC1 and N01, respectively, to apply corresponding polar impulses to thesecondary control line circuit, comprising controlline conductor CL1 andcontrol return conductor CR1 extending to the field station or stationsbeyond the repeater station. These iinpulses in line CL1 are repeated(irrespective of their polarity) by neutral relay FN1. c

A stepping relay bank comprising relays VP1, IV1 2V1 and LV1 areoperated by the impulses applied to the control line circuit in theoice. This stepping relay bank operates substantially in synchronismwith the stepping relay bank in the control office, with the exceptionthat relay LV1', which responds to the de-energization` of control linecircuit CL1 following they last impulse, is not released like thecorresponding relay Vin the control office but remains stuck up jandfunctions as a stored starting relay for initiating a second cycle ofoperations, following ,the receipt of a rst seresof indicationstransmitted from a .distant iieldstation and received in the repeaterstation. f

`Relay E11 responds tothe operation of the `stepl ping relay bank and isfor the purpose of pro- Viding stick circuits for relays MB1 and MF1 aswill be later pointed out.Y Relays MB1 and MF1 are message receivingrelays which correspond "to relays MB and MF respectively in the controloilice. Relays MB1 and MF1 receive the indications which are transmittedfrom a distant field station and cause these indications to be stored bystoring relays STO1, S1102, STO3 and STO4 during a particular cycle ofoperations. These storing relays are energized vin various combinationsin accordance with the indications received from a distant field stationduring a particular cycle and are stuck up until the next succeedingcycle, when these indications are transmitted to the control office inaccordance with the ombinations of storing relays which were energizedduring the previous cycle.

Relays FP1, 2FP1 and SA1 correspond to relays FP, 2FP and SArespectively in the control oice, that is relays FP1 and 2EP1 are pickedup and dropped in sequence in response to the impulses applied tocontrol line CL. Relay SA1 is picked up at the beginning of each cycle,remains up throughout the cycle and is dropped at the end of the cycle.K Relay SB1 is a repeater of relay SA1.

Relays PB1 and PF1 are for the purpose of applying indication impulsesto the indication line circut extending from the repeater station to thecontrol oilice during a cycle in accordance with the indications whichwere stored at the repeating station during a preceding cycle asmanifested by the particular combination of storing relays picked up.

Relay FC1 corresponds to relay FC in the control oflice in that it ispicked up in response to the initiation of a cycle from a eld stationand remains stuck up until the end of the cycle. Lock out relay L01 isprovided for the purpose of initiating the system in the control oice inresponse to a eld start condition at a distant iield station and inresponse to a stored Start condition at the repeater station. Relay L01is picked up to initiate an indication cycle and is dropped when such acycle is initiated from a distant eld station. During the consequentcycle the indications are transmitted from the distant field station andstored in the repeater station and at the end `of this cycle, relay L01is again picked up to initiate the system `through a second cycle ofoperations and to lock out all distant eld stations to prevent anydistant eld station transmitting indications during this second cycle ofoperations.

Resistance CRS1 is a charging resistance for charging the indicationline circuit extending from the repeater station to the distant stationsto apply a flow of charging y ning'of each period of an indication cyclewhich follows a period during which the indication line circuitincluding conductor IL1 has been conductively closed or opened at thefield station. Resistance IR1 is a compensating resistance forcompensating for the lower winding of relay L01 which is removed fromthe indication line circuit afterthe lock-out period of a cycle.

Field station equipment- Referring to Fig. .l

the eld station includes a biased-to-neutral current at the beginpolarline relay F2 and its repeating relays FP2,

SA2 and SB2, which operate in a similar manner to corresponding relaysin the control office, eX- cept that relay F2 `is a polar relay whilethe corresponding relay in the control cnice is a neutral relay. RelaySB2 is a repeater of relay SA2.

The eld'station includes a bank oi stepping relays IV2, 2V?,V LV2 andthe associated halt-step relay VPZ operating substantially insynchronism with corresponding relays at the repeater station inresponse to impulses applied to control line CLl and received by relayF2. The detailed circuits for operatingthe stepping relay bank and theline repeater relays are not shown since they may be the same as forcorresponding'relays in the control ofce and at the repeater station,with the exception that relay LV2 is released in the same manner asrelay LV in the control oi-Tice, that is at the end of each cycle. It isthus believed obvious that the line repeaterrelays and the steppingrelays operate in response to the operation ofl relay FP2 by means ofcircuits which are not shown but merely indicated by dotted lineconnection tions for the transmission of Relays PB2 and BF2 are similarto relays PB1 and PF1 at the repeater location. Relays PB2 and PF2 arecontrolled locally in accordance with local jumper connections and thepositions of local relay contacts. They function to condition theindication line ILl in accordance with the indications to be transmittedduring the different periods of a cycle as will be pointed out indetail.

Lock out relay L02 is picked up in response to a field start conditionat the illustrated station and it functions to energize indication lineIL1 for initiating a cycle of operations for the transmission ofindications from the associated station. Relay L02 furthermore locks outdistant field stations so that they are ineffective to apply impulses tothe indication line circuit during a cycle of operations for thetransmission of indications from the illustrated iield station.

Resistance IR2 is a compensating resistance for compensating for theresistance of the lower winding of .relay L02 which is removed from theindication line circuit after the lock out period. Resistance 2R2 is acompensating resistance to compensate for the value of resistance in theindication line circuit which is disconnected when a particular eldstation is transmitting. When the illustrated field station istransmitting, the indication line IL1 is connected to the indicationreturn line IRl by way of resistance 2R2, which resistance is of theproper value to compensate for the resistance of the indication linecircuit which would be completed at the end station of a series of fieldstations connected to the indication line circuit.

Track switch TS is illustrated as being controlled by switch machine SMin response to the operation of switch machine relay SMR. The occupiedand kunoccupied condition of the illustrated track section is repeatedby track relay T in the usual manner.

The control of the signals at the illustrated station has not been shownsince the control of the switch machinemay be considered typical of themanner in which additional steps of the cycle function to controlsignals in response to additional impulses. RelayV M is the usual signalrepeating relay which, when lde-energized as shown, indicates that allsignals associated with the illustrated track section are at stop andwhen energized indicates that some signal is clear.

Change relay CH2 is normally energized and is dropped (circuits notshown), in response to a changed condition at the associated eld stationfor initiating the system into a cycleV of operaindications.

The station selection portion of the system is not illustrated sincethis feature is immaterial for an understanding of the presentinvention. Station selection may be provided as explained in detail inthe abovementioned application Ser.

No. 640,062. .It need only be mentioned here that station relay SO2 ispicked up at the beginning of a control or duplex cycle and remains upthroughout the cycle at this station only when controls are to betransmitted to this station.

GENERAL OPERATION For convenience the control line circuit and theindication line circuit extending from the control oflice to therepeater stationl will be referred to as the primary controlflinecircuit and the primary indicationline circuit respectively. The controlline circuit and the indication line circuit extending from the repeaterstation to the distant field station will be referred y the control lineimpulses Y mitting indications originating "cations are being handled bythe to as the secondary control line circuit and the secondaryindication line circuit respectively. It will be understood that one ormore eld stations such as shown in Fig. 3 may be interposed in theprimary and/or secondary line circuits.

The repeater station of the present invention comprises a stepper and astorage portion. The stepper portion comprises the relays necessary toenable the repeater station to follow the cycles sent out from thecontrol ofce and to repeat received from the control oice. The stepperportion also includes relays necessary to enable the repeater station torespond to the secondary indication line impulses received from distantiield stations and also to impulse the primary indication line circuitin order to transmit indications to the control oiiice.

The storage portion of the repeater station includes relays which enablethe repeater to store indications received until it has an opportunityto transmit them to the control oiiice. The repeater station has its owncontrol line battery CB1 and indication line battery IB1 which furnishthe energy for the secondary control and secondary indication linecircuits respectively.

In the event that any one of the eld stations connected to the secondaryline circuit has new indications to transmit to the control cnice, the

transmitting eld station rst transmits these indications to the repeaterstation where they are stored. When a set of indications has been storedin the repeater no other indications can be transmitted to the repeateruntil it has transmitted the stored indications to the control oiiice,which it does on the cycle following the storage cycle, unless somesuperior eld station connected to the primary line circuit takes theline.

If there is a set of indications stored in the repeater station there isalso a start condition stored in the repeater station which will remaineiective until the repeater station is successful in transmitting itsstored indications to the control oice.

Indications can loev stored in the repeater station or transmitted fromthe repeater station to the control oiice by duplex operation, or if thesystem is not operated for controls a start is initiated automaticallyfor the purpose of transnected to the secondary line circuit.

The precharging .feature for the secondary indication line circuit isprovided at the repeater station and functions in the same manner as theprecharging feature oflice for the primary indication line circuit.

'I'he stepping and preconditioning of indications and other detailedoperations are performed in much the same manner as in an ordinarycontrol office and iield station with the exception that; first, whenthe repeater station is storing indications the stepping at the repeaterstation follows the line relay of the secondary line circuit, that isrelay FNI, and when the repeater station is transmitting storedindications to the control oiiice the stepping at the repeater stationfollows the line relay of the primary control line circuit, that isrelay F1. Second, when no indirepeater station, no stepping takes placeat the repeater station since only the line relays F1 and FNI, the codesending relays PC1 and N01 and the line repeating relays SAl and SB1operate.

The lock out feature at the repeater station at a station conl.

employed at the control functions the same as at an ordinary iield stav`tion. The repeater station is inferiorl to all stations connected ,tothe primary line circuits, which are located nearer the controloiiice,.and the repeater station is superior to all eld stationsconnected to the secondary line circuits. Thus the lock outfeature,.superiority, etc., of the field locations-.connected to thesecondary line circuits arel the same as for a control office and aseries of eld stations, the repeater station representing the controloice for the group- Qne or more repeater stations may be used asrequired. If more than one repeater station` is used Vthe controlsrarerepeated in the same `manner. as., illustrated yingfthe accompanyingdrawings Without any storage feature, Whilethe indications` are stored`rst in the repeater station of the group originating the startcondition, then in theA next repeater station and .finally transmittedtothe control ,office if the repeater stations are used-to extend thevmain/circuit. If the repeater stations are'used to.v handle branchlines extending from, a main line without repeaterstationsin Athe mainline, then the `repeater stations transmit directly tothe control oicesubject to thegeographic; superiority, butwithout the necessitypftransferring.; stored indications to any otherrepeaterstation. a f, YThe line circuits of a selector system such as r disclosed in the abovementioned application Ser.

. indication return conductor No. 640,062 comprise a Acontrollinecircuit including control line conductor CL and control return`conductor CRfand an indication line circuit including indication lineconductor IL and 1R..V 4,'Ihesetwo line circuits correspond Vto 'thevcontrol line circuit including conductors I and I2 yandtheindication'linefcircuit including conductors I4 and vll in the abovementioned prior application. In a system of this character the control;line conductor CL is connectedv to the control return, con-y ductorCR.-V at the ,last field station associated with the primary linecircuit, with the line relays of` any field station or stations betweenthe re,- peater stationand the control oliice, as -well as thelinerelays Vat-the control oiceand at the repeater station connected in,series with the control line wire.,

The primary line circuit is energized with positiveand negative impulsesfrom a control line battery in the control oilce for the purpose oftransmitting controls and for the purpose of causing the synchronousstep-by-step operation at the controloilice and at the stations as willbe later explained.

The primary indication line circuit is energized from, an indicationline, batteryV in the control office, having includedv therein 4`at thecontrol office message receiving relays, MF and MB which are controlledthrough trontand back contacts Yrespectively of relays Fl" and ZEP, aswell as through` `contacts of relays PC and NC. The primary indication'line conductor IL extends to all of the iield stations connected to the`primary line `circuits and normally includes a back Contact, such asback contact 255 of relay LO2 of Fig. 3, at any station located betweenthe oi'lice and the repeater station. In the present embodiment theprimary indication line conductor terminates at `front contact ist ofrelay L01 at the repeater station. 1w i When a particular field stationvis transmitting= the lock outl relay at the associated station is pickedup thereby rendering the open or closed conductive condition of the`primary indication line circuit with which the transmitting station isassociated, dependent upon the control of either a relay similar torelay PE2 or PB2 of Fig. 3 in accordance with whether the primarycontrol line circuit is energized or deenergized. It will be understoodthat the above discussion assumes that one or more field stations areconnected to the primary line circuits between the repeater station andthe control ollice.

A similar condition exists with regard to the secondary control andindication line circuits extending from the repeater station to thedistant eld station or stations, that is the secondary control vlinecircuit includes `line relays at these distant stations with the controlline conductor CL1 permanently connected to the return line conductorCB1 at the end station. The lock out arrangement and the conditioning ofthe secondary indication line circuit by the PB2 and PE2 relaysassociated with the secondary in.- dication line circuit is similar tothe functions of corresponding relays associated with the primaryindication line circuit, with the secondary indication line circuitnormally open ended at the last station.

DETAILED OPERATION Normal marittima-With the system in its normalcondition as indicated in the accompanying drawings, the primary controlline circuit "I' and the secondary control line circuit are bothdeenergized. The primary indication line circuit and the secondaryindication line circuit are both normally held open. All relays in thecontrol oflice and at the repeater station are normally deenergized. Allrelays at the ield station (Fig. 3) are likewise normally deenergizedwith the exception of track relay T which is illustrated in its pickedup condition, since it is assumed that the associated `track section isunoccupied. Change relay CH2 is likewise illustrated in its pickedupcondition since it is assumed that a field start has not beenvinitiated.

For convenience in describing the operations 1 which follow, the controlline circuits will be referred to as on periods, while the deenergizedor time space periods between impulses will be referred to as ofiperiods. The system will be described as stepping through cycles, eachcomprising a conditioning on period, a rst off period, a rst on period,a second oir period, a second on period and a third clearing out offperiod.

Manual start-It will rst be assumed that the operator in the controloffice desires to move track switch TS at the eld station, illustratedin Fig. 3i, from its normal locked position to its reverse lockedposition. It will be assumed that the illustrated eld station respondsto a code combination of (-1-) and on the rst two steps of thecommunication system. It will also be assumed that the trackswitch isoperated to its reverse position in response to a impulse on the thirdstep of the system.

With the system in its normal condition the actuation of starting buttonSB in the control oirlce is effective to pick up relays C and CD forinitiating a control cycle. Since the detailed circuit arrangement forcontrolling the VC and CD relays is immaterial for an understanding ofthe present invention it has been omitted from the present disclosure,but this circuit arrangement may be the same as disclosed in the abovementioned application Ser. No. 640,062. It will be understood that onlyone CD relay can be picked the energized or impulse periods of up atanyone time and only at the time system is in its normal condition.

VThe picking up of relays CD and C closes a circuit Vfor picking uprelay PC which extends fi'om'K-Il), back Contact d0 of relay E, frontcon-V tact 4I of relay C, back contacts 43 and 44 of relays 2V and IVrespectively, conductor 45, front contact 46 of relay CD, code jumper 5,PC bus 4l and winding of relay PC to Y impulsing and steppingoperations-The pickthe ' ing up of relay PC energizes the primarycontrol line circuit with a impulse to mark the beginning of theconditioning on period. This circuit extends from the (I-) terminal ofbattery CB, front contact 5| of relay PC, back contact 5t of relay NC,winding of relay F, primary control line conductor CL, winding of relayF1, primary control return conductor CR, back contact 50 of relay NC andfront contact 5310i relay PC to the terminal of battery CB.

This energization 'of the primary control line circuit picks up relay Fand positions the polar contacts of relay F1 to the right. Relay Fcloses an obvious pick-up circuit for relay FP at its front contact 61,relay FPcloses an obvious pickup circuit for relay EFP at its frontcontact 63 and relay EFP closes an obvious pick-up circuit for relaySAat its front contact 59.

Relay F1 closes an obvious pick-up circuit for relay PC1 at contact |61in its right hand dotted position. Relay F1 closes a pick-up circuit forrelay SA1 which extends from contact |60 of relay F1 in its right handdotted position, .back contact IGI of relay FCl, back contact |62 ofrelay L01 and Winding of relay SA1 to Since neither relay F01 nor relayL01 is picked up during a control cycle, the above described circuit forrelay SA1 is intermittently energized by the intermittent operation ofcontact I 60 of relay Fl in response to the control impulses applied tothe primary control line circuit, which maintains relay SA1 picked upuntil the end of the cycle. Relay SA1 closes an obvious pick-up circuitfor relay SB1 at its front contact |63 which maintains relay SB1 pickedup until the end of the cycle.

The picking up of relay PC1 energizes the secondary control line circuitwith a impulse over a circuit extending from the (-l-) terminal ofbattery CB1, front contact I5I of relay PC1, back contact |54 of relayNC1, winding of relay llNl, control line conductor CLI, winding of relayF2, control return conductor CRl, back con' tact |50 of relay NC1 andfront contact |53 of relay PC1 to the terminal of battery CB1.

Relay FNl is picked up over the secondary control line circuit and relayF2 actuates its polar contacts to the right. Since relay F01 at therepeater station is not picked up during a control cycle the operationof relay FN1 during such a cycle is ineiective because of open front contact I 64. Y

At the field station, the actuation Vof contact 26IV of relay F2 to theright closes an obvious pick-up circuit for relay FP2.V Although thedetailed circuits are not showin Fig. 3, in ac-V cordance with theoperation of the system disclosedin the above mentioned application Ser.No. 640,062, the conditioning (-I) impulse applied to the secondarycontrol line effects the pick-up of the station relays at a portion ofthe eld stations, such as relay S02 of Fig. 3. Thus, due to theactuation of contact 2I4 of relay F2 to the right, it will be assumedthat relay S02 is picked up and remains in its picked up condition inresponse to the station selecting impulses applied to the line circuitsfor selecting the station illustrated in Fig. 3, so that the rst controlimpulse following station selection will be eiective at Athe illustratedfield station due to closed front contact 2| 5 of relay SO2.

As above mentioned the detailed circuits for controlling relays SA2,SB2, VP2, IV2, 2V2 and LV2 at the eld station have been omitted, sincethis control may be elected in the same manner disclosed in the abovementioned application Ser. No. 640,062 and indicated in the presentdrawing by dotted line 265. 1

During the impulsing of the primary control line circuit which follows,the stepping relay bank at the repeater station is not operated becauseof open front contacts |52 and |55 of relays L01 and PC1 respectively.

The energization of the primary and secondary control line circuits asabove described is elective to provide the lconditioning on period ofthe cycle. During this on period relay VP in the control oce is pickedup overa circuit ex tending from front contact 'II of relay SA, frontcontact 'I2 of relay 2FP, back contacts 85 and I3 of relays 2V and IVrespectively and winding of relay VP to Relay VP closes a rst stickcircuit for itself extending from front contact II of relay SA, frontcontact I4 of relay VP, back contacts and 'I3 of relays 2V and IVrespectively and winding of relay VP to The picking up of relay VPcloses an energizing circuit for relay E which extends from frontcontact of relay SA, back contacts 3| and 32 of relays 2V and IVrespectively, front contact 33 of relay'VP and winding of relay E to Thepicking up of relay E opens the circuit of relayiPC at its back contact40. Relay PC drops and opens the control line circuit to mark the end ofthe conditioning on period and the beginning of the first olf period.This drops relays F, FP and 2FP in sequence in the control office.Relays F1 and PC1 at the repeater station are de-energized in sequence,the dropping of relay PC1 deenergizing the secondary control linecircuit which is effective to drop relays F2 and FP2 at the fieldstation. 0f course relay FNl responds to the impulses in the secondarycontrol line circuit but since this relay is ineffective during acontrol cycle its operation will not be further mentioned during thedescription of the control cycle operation.

'Ihe dropping of relay 2FP in the control office closes a circuit forpicking up relay IV which extends from (-1-) front contact 'I5 of relaySA, back contact 'I6 of relay 2FP, front contact 'I'I of relay VP, backcontact 'I8 of relay 2V and winding of relay IV to Relay IV closes astick circuit for itself extending from (f-), front contact 'I5 o frelay SA, front contact 'I9 and winding of relay IV to This stickcircuit for relay IV is maintained energized until relay SA is droppedat the end of the cycle. It will be obvious that relays 2V and LV, whenpicked up, close similar stick circuits for themselves at their frontcontacts 83 and 84 respectively and it will not be necessary to pointout the closure of these stick circuits again during the operation ofthe system, since these stick circuits are likewise maintained energizeduntil the end of the cycle.

'I'he picking up of relay IV opens the first stick circuit of relay VPyat back contact 13, but prior toI this a second stick circuit is closedfor relay VP which extends from front contact acetico 1I of relay SA,back contact 12 of relay` 2FP, front contact 85 and winding of relay VPto The picking up of relay IV de-energizes relay E at back contact 32and the dropping of relay E picks up relay NC over a circuit extendingfrom back contact l5 of relay E, front contact 4I of relay C, backcontact i3 of relay 2V, front contact 4i of relay iV, conductor 56,front contact 51 of relay CD, jumper 6, NC bus 48 and winding of relayNC to l The primary control line circuit is therefore energized with aimpulse over a circuit which now extends from battery CB through backcontacts 5I and 53 oi' relay PC and front contacts 5@ and 5iof relay NC,which contacts reverse the connection of the battery applied to theprimary control line circuit from that previously pointed out.

The energization or" the primary control line circuit effects thepicking up of relays F, FP and 2FP in the control office, positioning ofthe polar contacts of relay F1 at the repeater station to the left andthe picking up of relay NCl over an obvious circuit closed at contact|61 of relay F1 in its left hand dotted position. With relay NC1 pickedup and relay PC1 down the secondary control line circuit is energizedwith a impulse.

The picking up of relay ZFP in the control oii'ice drops relay VPbecause the first stick circuit for relay VP is open. at back contact 13of relay IV and the second stick circuit for relay VP is open at backcontact 12 of relay ZFP. The dropping of relay VP closes a circuit forpicking up relay E which extends from (-I) iront contact 9i! of relaySA, back contact 3l of relay 2V, front contact 32 of relay IV, backcontact 33 of relay VP and Winding of relay E to the primary control Thepicking up of relay E de-energizes the above traced circuit for relay NCwhich drops and de-energizes the primary control line circuit to markthe end of the first on period. Relays F, FP and are dropped in sequenceand relay 2V is picked up over a circuit extending from front contact 15of relay SA, back contact 15 of relay liFP, back contact 11 of relay VP,front contact 32 of relay IV and winding of relay 2V to The picking upof relay 2V de-energizes relay E at back Contact 3l and the dropping ofrelay E energizes relay NC which in turn energizes line circuit to markthe beginning of the second on period.

^ Relays F, FP and 2FP are picked up in sequence and relay VP is pickedup over a circuit extending from iront contact 1I of relay SA, frontcontactJ 12 of relay iront contact 85 of relay 2V and winding relay VPto Relay VP again completes and prepares its stick circuits which arebelieved to be obvious and unnecessary to be pointed out again.

The picking up of relay VP energizes relay E over a circuit extendingfrom (-I-), front contact Si! of relay SA, iront contacts 3l and 33 ofrelays 2V and VP respectively and winding of relay E to The picking upof relay E de-energizes relay NC which drops and de-energizes theprimary control line circuit to mark the end of the second on period andthe beginning of the third or releasing out ofi period. Relays F, FP and2FP are dropped in sequence and relay LV is picked up over a circuitextending from front contact 15 or relay SA, back contact 1E of relayZFP, front contact i1 of relay VP, front contact 18 of relay 2V andwinding oi relay LV to The picking up of relay LV does not change thecircuit condition of relay E, therefore this relay remains up, the PCand NC relays remain down and the primary control line circuit remainsdeenergized so that relay ZFP remains down for a suiiciently long periodto drop relay SA and clear out the circuits. The dropping of relay SAde-energizes relays E, VP, IV, 2V and LV` by the opening of its frontcontacts 90, 1I and 15. The dropping of relay SA also de-energizesrelays CD and C, by circuits not shown in the present disclosure.

When relay 2V was picked up during the second ofi period as abovedescribed, its contact 43 shifted the energizing circuit from conductor56 to 5I, which extends this circuit through front contact 62, lever SMLin its right hand dotted line (reverse) position and NC bus 43 to thewinding of relay NC. This is effective to make the third impulse appliedto the primary control line circuit during the second on period It willbe understood that lever SML in its left hand (normal) position wouldenergize relay PC instead of relay NC, so that the switch controlimpulse would be instead of Referring to the field station illustratedin Fig. 3 it will be recalled that the (-I) and irnpulses applied to theprimary control line circuit are repeated into the secondary controlline circuit by the operation of relays PCl and NC1 respectively at therepeater station. It will be understood that the conditioning and thefirst impulses which were assumed to be and because of the connectionsof jumpers 5 and 6 in the control o-iiice, were effective to select thestation illustrated in rig. 3 by maintaining relay SO2 in its energizedcondition.

After the station is selected the third impulse (second 0n) which wasapplied to the secondary control line circuit in response to the impulseapplied to the primary control line circuit (because lever SML wasassumed to be in its reverse position), positions contact 2 It of relayF2 to the left. This closes a circuit for energizing relay SMR extendingfrom (CN), winding of relay SMR, front contact 2 i6 of relay 2V2, frontcontact 2 I5 of relay SO2 and contact 2 I4 of relay F2 in its left handdotted position to (B This positions contact 256 of relay SMR to itsleft hand dotted position for controlling the operation of the switchmachine for actuating the track switch to its reverse locked position.

It will be apparent that a impulse received at the iield station duringthe second on period would position contact 2M of relay F2 to the right,which would energize relay SMR in the i opposite direction forpositioning contact 250 to the right for controlling the switch machineto actuate the track switch to its normal locked position.

It will be understood that relays F2 and FP2 which follow the impulsesin the secondary control line circuit remain cle-energized at the end ofthe cycle for dropping relays SA2, S32, the stepping relays and relaySO2. Likewise, relays SA1 and SBl at the repeater station are droppedduring the clearing out period because contact i60 of relay F1 remainsin its neutral position for a comparatively long interval of time whenthe secondary control line circuit is cle-energized at the end of thecycle.

INnrcAfiIoNs Automatic start-Assuming the system to be in its normalcondition when a change in condition occurs at a iield station, forexample the station illustrated in Fig. 3, relay CH2 is dropped inresponse tosuch a change in condition. This closes a circuit for pickingup relay L0.2 which extends from (Jp), back contact 261 of relay FP2,back Contact 238 of relay SB2, back Contact 253 of relay SA2, upperwinding of relay L02 and back contact d of relay CH2 to Relay L02establishes a substitute circuit to at its front contact 255 which isindependent of back contact 25d of relay CH2.

The secondary indication line circuit is enerv gized in response to thepicking up of relay L02 iii) over a circuit extending from the terminalofV battery IB1 (see Fig. 2C), lower winding of relay MB1, back contacts|58 and |59 of relays SB1 and LV1 respectively, indication lineconductor IL1, front contact 255 of relay L02, back contact 212 of relaySB2, lower winding of relay L02, resistance R2 and indication returnconducto-r TR1 to the terminal o-f battery IB1.

Relay MB1 Vis picked up over the above described circuit and a circuitis closed for picking up relay FC1 which extends from (-1-), frontcontact |65 of relay MB1, back contact IBS of relay SB1 and winding ofrelay FC1 to The picking up of relay FC1 closes a circuit for picking uprelay L01 which extends from back contacts |68, |59 and |10 of relaysFP1, SB1 and SA1 respectively, upper winding of relay L01 and frontcontact |1| of relay FC1 to The picking up of relay L01 closes theprimary indication line circuit over a circuit eX- tending from theterminal of battery IB (see Fig. 1B), lower winding of relay MB, backcontacts S28 and 91 of relays PC and NC respec tively, back contacts $4and 92 of relays FP and EFP respectively, front contacts 9| and 8| ofrelays SA and FC respectively, indication line conductor IL, frontcontact |56 of relay L01, back Contact i12 of relay SB1, back contact|13 of relay FP1, lower winding of relay L01 and indication returnconductor IR to the terminal of battery IB.

The closing of the primary indication line circuit picks up relay MBwhich in turn closes a circuit for picking up relay FC at its frontcontact 33. The pick-up and stick circuits of relay FC have been omittedfrom the drawings for the sake of simplicity, since the detailedoperation of this relay is immaterial for an understanding of theYpresent invention, it being understood that these circuits can be thesame as disclosed in the above-mentioned application Ser. No. 640,062..

Repeater stepping opwarmen-The picking up of relay FC closes a circuitfor picking up relay NC which extends from (-l-), back contact 4|) ofrelay E, back contact 4| of relay C, front contact of relay FC, NC bus48 and winding of relay NC to It will be assumed that this is a cyclefor the transmission of indications alone (not a duplex cycle), so thatrelay C remains down and relay FC remains picked up for maintainingrelay NC energized throughout the cycle. This provides a series ofimpulses applied to the primary control line circuit over a circuitextending through front co-ntacts and 54 of relay NC and back contacts5| and 53 of relay PC.

The energization of relay NC energizes the primary control line circuitwith a conditioning impulse which effects the picking up of relays F,FP, ZFP, SA, VP and E in the same manner as previously described.

The picking up of relay E drops relay NC which de-energizes the primarycontrol line circuit to effect the dropping of relays F, FP, EFP and thepicking of relay |V, which in turn drops relay E for again picking uprelay NC which in turn energizes the primary control line circuit with aimpulse,

It is believed unnecessary to pointout in detail how the step-by-stepoperations in the control oice and atthe field station (Fig. 3) areeffected, since these operations are the same as already described inconnection with a control cycle, with the above mentioned exceptionthatthe primary control line circuit is energized with a series of impulses.This positions the polar contacts of relay F1 at the repeater station tothe left for each impulse which picks up relay NC1 to repeat a series ofimpulses into the secondary control line circuit.

During the step-by-step operations relay FN1 at the repeater stationfollows the impulses applied to the secondarycontrol line circuit. RelayMB is dropped when relay EFP is dropped during the rst olf period of thecycle. The stick circuits for relays MB and MF will be later pointedout. Since the primary indication line circuit is not energized duringthis rst indication cycle relay MB (as well as relay MF) remains downthroughout this first cycle.

The conditioning impulse applied to the primary control ondary controlline circuit with a impulse for picking up relay FN1. Relay FN1 closes acircuit for picking up relay FP1 which extends from front contact |14 ofrelay FN1, front contact |66 of relay FC1 and winding of relay FP1 toRelay FP1 closes a circuit for picking up relay 2FP1 which extends fromfront contact |15 of relay FC1, winding of relay 2FP1 and front contact|16 of relay FP1 to The picking up of relay FP1 opens the primaryindication line circuit at back contact |13 and since relays PF1 and PB1are not operated during this first indication cycle the primaryindication line circuit remains open throughout the cycle because ofopen front contacts 11 and |18 of relays PF1 and PB1 respectively.

The picking up of relay FP1 opens the local energizing circuit includingthe upper winding of relay L01 at back contact |68 and, since theenergizing circuit through the lower winding of relay L01 is open atback contact FP1 and back contact |19 of relay FC1, relay L01 isdropped. This opens the primary indication line circuit at front contact|56, at which point it remains open throughout this rst indicationcycle.

Relay FC1 is stuck up throughout the first indication cycle over anobvious circuit to at front contacts |41 and |415 in multiple of relaysSA1 and 2FP1 respectively. Relay MB1 is dropped during the conditioningon period in response to the opening of the secondary indication linecircuit by the picking up of relay SB2 at the station of Fig. 3. This isbecause the secondary indication line circuit is opened before relay SB1is picked up to close the stick circuit for relay MB1 at front contact|38.

From the above it will be observed that a change in condition at a ieldstation is effective through a cycle during which the primary indicationline circuit is not conditioned. It will now be explained how thesecondary indication line circuit is conditioned for transmittingindications to the repeater station where they are received and stored,after line circuit energizes the sec- |13 of relay 4tioning on appliedto which a second indication cycle is effected for the transmission oithese stored indications to the control oiiice.

The picking up oi relay 2FP1 as above described. closes a circuit forpicking up relay SA1 which extends from (J,), iront contact |58 of relayFP1, conductor 25|), front contact |85 of relay FC1, front contact iiilof relay 2FP1 and Winding of relay SA1 to Relay SA1 closes an obviouspick-up circuit for relay S131 at its front contact |63.

Relay VP1 is now picked up over a circuit extending frorn (-1-), frontcontact |51 of relay SB1, front contact |55 of relay FC1, front contact|82 of relay FP1, back contact |33 of relay |V1 and Winding of relay VP1to Relay VP1 closes a first stick circuit for itself including the abovedescribed circuit and by vvay oi` front contact |85 of relay VP1, whichcircuit is independent of contacts |55 and |82 of relays FC1 and FP1respectively.

In response to the termination of the condithe secondary control linecircuit, relays FN1, FP1 and 2FP1 are deenergized in sequence. It willbe observed that stepping at the repeater station is controlled bycontact |15 of relay FN1, contact |55 of relay F1 being ineffectivebecause of open contact |E| of relay FC1.

A circuit is now closed for picking up relay |V1 which extends fromiront contact |51 of relay SE1, front contact |55 of 'relay F01, backcontact |32 of relay FP1, iront contact |555 of relay VP1, back contact|55 of relay 2V1 and winding of rela?,T |V1 to Relay FP1 closes a secondstick circuit for relay VP1 to prevent this relay being dropped duringthe 01T period, which circuit extends from (-l-) iront contact |81 oirelay SE1, back contact |88 of relay FP1, iront contact |89 and Windingof relay VP1 to The picking up of relay |V1 closes a stick circuit foritself extending from front contact |51 of relay SB1, iront contact 95and winding of relay |V1 to Relay E1 is picked up during theconditioning on period over a circuit extending from iront Contact Veiloi relay SB1, iront contact |92 of relay F01, back contact |53 of relayZV1, back contact iifi or" relay |V1, front contact |95 oi relay VP1 andwinding of relay E1 to in response to the picking up of relay |V1 duringthe first ofi period the above described circuit for relay E1 is openedat back contact itt which effects the release of relay E1.

In response to the termination of the first ofi period and the beginningoi the first on period applied to the secondary control line circuit,relays FN1, FP1 and 2FP1 are picked up in sequence. Relay VP1 is droppedduring this on period because its first stick circuit is open at backcontact |133 of relay |V1 and its second stick circuit is open at backcontact |88 of relay FP1. Relay E1 is now picked up over the abovedescribed circuit which now extends through back contact |95 oi relayVP1 and front contact |S of relay |V1.

In response to the termination of the rst "on period and the beginningof the second off period relays FN1, FP1 and 2FP1 are dropped insequence. Relay ZV1 is picked up over a circuit extending irorn irontcontact |51 of relay SB1, iront contact of relay FC1, back contact |62oi relay FP1, back contact |85 of relay VP1, iront contact |55 of relay|V1 and winding of relay ZV1 to Relay ZV1 closes an obvious stickcircuit for itself at its front contactv|91. Relay E1 is dropped duringthis ofi period because of open back contact |93 of relay ZV1.

In response to the termination oi the second ofi period and thebeginning of the second on period relays FN1, FP1 and 2FP1 are picked upin sequence. Relay VP1 is now picked up over a circuit extending from(-1-), front contact |51 of relay SB1, front contact |55 of relay FC1,front Contact i82- of relay FP1, iront contact |98 of relay 2V1 andwinding of relay VP1 to Relay VP1 closes its rst stick circuit at itsfront contact |84 and prepares its second stick circuit at iront contact|89, which circuits are obvious from the previous explanation. Relay E1is picked up over the above described pick-up circuit which now includesfront contact |93 of relay ZV1 and iront contact |95 of relay VP1.

In response to the termination of the second on period and the beginningof the third oit period relays FN1, FP1 and 2FP1 are dropped insequence. A circuit is now closed for picking up relay LV1 which extendsfrom (-1-) front contact |51 of relay SB1, front contact |55 of relayFC1, back contact |32 of relay FP1, front contact |85 of relay VP1,front contact |85 of relay 2V1 and lower winding of relay LV1 to RelayLV1 establishes a stick circuit for itself which extends from backcontact |99 of relay L01, iront contact |49 and upper winding of relayLV1 to Since relay L01 remains down throughout this first cycle and isnot picked up until the beginning of the second indication cycle orpossibly a later cycle when the repeater station is allowed to transmit,relay LV1 is maintained stuck up during the clearing out period betweencycles by a circuit extending to at back contact |48 of relay ZV1.

The third oir period marks the end of the first indication cycle, sincethere are no further impulses applied to the primary control linecircuit in the control oiiice, so that relay 2FP1 remains down for aperiod of time sucient to allow all slow repeater relays to release.Relay SA1 drops which in turn deenergizes relay SB1 at open frontcontact |63 and the dropping of relay SB1 deenergizes relays VP1, |V1and ZV1 at open front contacts |51 and |81. Relay SA1 deenergizes relayF01 at open front contact |41.

The opening of front contact |92 of relay F01 deenergizes relay E1.

Transmission of indications to `repeater station.-During the operationof the rst indication cycle above described, indications are transmittedfrom the iield station illustrated in Fig. 3 to the repeater stationillustrated in Figs. 2A, 2B and 2C by the conditioning of the secondaryindication line circuit. Relays LOZ and SB2 remain picked up at the eldstation throughout this first indication cycle so that the circuit ofthe secondary indication line including front contact 212 of relay SBZ,can be energized or deenergized during both the on" and off periods asselected by contact 213 of relay FP2 in accordance with the closed oropen conditions of contacts 295 and 29| of relays PF2 and FB2respectively. l

During each ofi period in the series ofv impulses the (-1-) terminal ofindication battery 1B1 (Fig. 2C) is connected tosecondary indicationline conductor IL1 through the lower winding of relay MB1 and currentflow in the secondary indication line circuit is dependent upon frontcontact 29| of relay FB2. More specically, relay PB2 is the codetransmitter for of the series. Assuming jumper 289 at the iield stationto be connected to (-1-) as shown, relay FB2 is picked up during theconditioning on period over a circuit extending from (-1-), jumper 239,back contacts 295 and 286 of relays IV2 and 2V2 respectively, irontcontact 288 of relay FP2, winding of relay FB2 and front contact 289 ofrelay L02 to The picking up of relay FB2 provides one of a choice of twooff indication codes.

When relay FP2 is dropped during the first on period relay FB2 is stuckup over a circuit extending from (-1-), iront contact 299 of relay FB2,back contact 283 oi relay FP2, winding of relay FB2 and front contact289 of relay L02 to When relay FP2 is picked up during the rst on periodthe above described stick circuit is opened and the energization ofrelay FB2 is dependent upon a circuit extending through front contact285 of relay W2 for the second olif indication, to contact 292 of relayT, which being open illustrates the alternate choice of an offindication. Relay FB2 will be deenergized.

During the second on period the energization of relay FB2 is dependentupon the energization of a circuit including front contact 286 of relay2V2, which circuit has not been shown because the above examples aretypical of the choice of two conditions for the transmission of oliindications.

With relay FB2 picked up during the conditioning on period and stuck upthroughout the rst 01T period as above described, the secondaryindication line circuit is closed as will be presently pointed out. Thisindication line circuit Was opened during the conditioning on periodwhen relay SB2 opened its back contact 272.

The lock out period for maintaining relay L02 energized extends from thetime of the picking up of relay FP2 and the consequent opening of itsback contact 297 until the picking up of relay SA2 and the consequentclosing of its front contact 253, during which period relay L02 isdependent for its energization on line current received from battery IB1at the rep-eater station and through its lower Winding. In the eventthat some other station superior to the station of Fig. 3 opens thesecondary indication line circuit during this lock out period, then ofcourse relay L02 is dropped during the lock out period and it cannot bepicked up again until the start of another cycle. With relay L02maintained picked up during the lock out period, then when relay SA2closes` its front contact 253, relay L02 is stuck up over a circuitincluding its upper winding and its front contacts 255 and 258 in serieswith iront contact 253 of relay SA2. Thus relay L02 is maintained pickedup until relay SA2 drops at the end of the cycle.

During each on period the secondary indication line circuit remains openor is closed depending upon contact 299 of relay PF2. For example,assuming that code jumper 282 is connected to (-1-) as shown in Fig. 3,then relay FP2 is picked up during the rst off period over a circuitextending from (-1-), jumper 282, back contact 294 of relay 2v2, frontcontact 295 of relay VF2, back contact 297 of relay FP2, winding ofrelay PF2 and front contact 289 of relay L02 to When relay FP2 is pickedup during the first on period relay PF2 is stuck up over a circuitextending from (-1-), iront contact 298 of relay PF2, front contact 297of relay FP2, Winding of 4relay PF2 and front contact 289 of relay L02to The abovev illustrates one choice of an on indication Whereby relayP1212 is picked up. The other choice of an on indication is effected bythe Ideenergization of the circuit including the Winding of relay PF2and back contact 227 of relay FP2. The first choice on indication againenergizes relay PF2 in the second oi period, While the other choice onindication does not eiect the picking up of relay PF2 during an oilperiod so that it is down throughout the following on period.

Since relay M is assumed to be deenergized and its back contact 29!closed, the econd on indication is the same as the iirst on indicationbecause relay BF2 will be picked up during the second olf period over acircuit extending through back contact 29! of relay M, iront contact 293of relay lV2, back contact of relay VP2 and back contact 297 of relayFP2 to the winding of relay PF2. The third on indication is selectedthrough front contact 2913 of relay 2v2, which circuit is not shownsince it is believed the above examples are suiiicient to illustrate thechoice of two on indications which may ce provided at each step of thesystem,

It will now be explained how the conditioning of relays FB2 and PF2effects the closing and the opening of the secondary indication linecircuit for transmitting indications to the repeater station Where theyare received and stored.

From the above discussion of the conditioning of the FB2 and PF2 relaysit will be observed tha' relay FF2 is positioned during an oil period inaccordance with the indication it is to transmit in the next on period,While relay FB2 is positioned during an on period in accordance with theindication it is to transmit in the next olif period. Thus on each steptaken by the step-by-step mechanism at the field station relays PF2 andFB2 govern the secondary indication 'ne circuit.

It will be recalled that the secondary indication line circuit wasopened during the conditioning on period by the picking up of relay SB2andthe consequent opening or its back contact 272. The dropping of relay2FP1 at the repeater station during the iirst oli period permits currentto iloW in the secondary indication line circuit (because relay FB2 ispicked up throughout this off period), over a circuit extending from the(-1-) terminal of battery IB1 at the repeater station, lower winding ofrelay MB1, back contacts iili and l of relays P01 and NC1 respectively,back contact i152 of relay FP1, back contact lll! of relay 2FF1, irontcontact M9 of relay SA1, iront contact E52 oi relay SB1, back contact 59of relay LV1, secondary indication line conductor IL1, front contacts256 and 272 of relays L02 and SB2 respectively, back contact 273 oirelay FP2, front contact 29! of relay FB2, resistance 2R2 and indicationreturn conductor IRl to the terminal of battery IBI,

This energization of the secondary indication line circuit picks uprelay MB1 and it is stuck up over a circuit extending from (-1-), frontcontact I or relay 5B1, back contact 939 of relay E1, front contacti355- and upper Winding' of relay MB1 to During the iirst on period thepicking up oi relay ZFPl (before the picking upI of relay E1) closes asubstitute stick circuit for relay MB1 which extends through frontcontact 39 of relay SE1 and front contact i3! of relay 2ER Relay MB1 isthus stuck up when picked up throughout the "on period following the offperiod during which it was picked up.

The picking up of relay N01 at the repeater station to mark thebeginning of the iirst on period opens the secondary indication linecircuit at back contact |43. This deenergizes the secondary indicationline circuit and when relay 2FP1 is picked up during the rst on periodthe secondary indication line circuit is again energized because relayPF2 at the field station is up.

The energizing circuit for the secondary indication line circuitextendsV from the (-1-) terminal of battery IB1, lower winding of relayMF1, back contact |35 of relay PC1, front contact |36 of relay NC1,front contact |31 of relay FP1,rfront contact |l|| of relay 2FP1, frontcontact |4 of relay SA1, front contact |58 of relay SB1, back contact|59 of relay LV1, indication line conductor IL1, front contacts 256 and212 of relays LO2 and SB2 respectively, front contacts 213 and 299 cirelays FP2 and PFZ respectively, resistance 2R2- and indication returnconductor IR1 to the terminal of battery IB1. This eiects theenergization of rel-ay MF1 and since relay E1 is picked up during thisfirst on period, relay MF1 is stuck up over a circuit extending fromfront contacts |30 and |33 of relays SB1 and E1 respectively, frontcontact |38 and winding of relay MF1 to When relay 2FP1 is droppedduring the succeeding (second) off period relay MF1 is stuck up over acircuit including back contact |3I of relay 2FP1. It will thus beobserved that relay MF1 when picked up during an on period is stuck upthroughout the following oif period. The dropping of relay 2FP1 duringthe second off period fails to close the secondary indication linecircuit because of open front contact 29| of relay PB2. 1

When relay 2FP1 is picked up during the second "on period then thesecondary indication line circuit is closed because relay PF2 is pickedup throughout this period. It is believed unnecessary to trace theenergizing circuit for the secondary indication line since it is thesame as previously traced.

Since the secondary indication line circuit is not energized during thesecond oif period in response to the dropping of relay 2FP1, relay MB1is dropped during this period when relay 2FP1 opens its front contactI3| because the stick circuit for relay MB1 is de-energized at open backcontact |33 of relay E1 and open front contact |3| of relay 2FP1.

The energization of the secondary indication line circuit during thesecond on period picks up relay MF1 as previously described and thisrelay is stuck up for a sufcient period of time during the following offperiod to execute this particular indication condition. In the eventthat relay PF2 is down throughout the second "on period the relay MF1 isdropped when relay 2FP1 opens its back contact |3| to de-energize thestick circuit of relay MF1 before it is energized by the closure offront contact |33 of relayE1.

During the last off (clearing out) period the secondary indication line`circuit Vis de-energized by the dropping of relay NC1 and the openingof its front contact |355. Relay MF1, which was stuck up throughout thesecond on period, is dropped in the lclearing out period when relay SB1drops and opens its front contact |30. Relay PFZ, which was stuck upthroughout the second on period, is dropped when relay FP2 drops andopens its front contact 291 in the clearing out period.

From the above it will be observed that relay MB1 is selectivelyresponsive during the oif periods to the energization andde-energization of the secondary indication line circuit for receivingeither one of a choice of two distinctive indications, with the selectedchoice maintained throughout the following on period by relay MB1 eitherbeing up or down throughout this on period. Furthermore, relay MF1 isselectively responsive during each on period in accordance with oneoranother choice of two indications transmitted during each on period,with relay MF1 remaining up or down throughout the following off periodto register the selected indication which was transmitted and receivedby this relay.

Storage of indications. -Storage relays STO1 and STO3 store the offindications received by relay MB1 and storage relays STO2 and STO4 storethe on indications received by relay MF1. It will be understood thatadditional storage relays may be provided when additional steps are usedat the repeater station.

It will be recalled that relay MB1 was maintained in its picked upposition throughout the first on period in accordance with theindication received in the previous o period. With relay MB1 picked up acircuit is closed during the first on period for energizing relay STO1which extends from front contacts |20 and |2| of relays MB1 and FP1respectively, front contact |22 of relay F01, back contact |23 of relay2V1, front contact l2@ of relay |V1 and winding of relay STO1 to RelaySTO1 closes a stick circuit for itself extendingfiom (-i-) front contact|39 of relay SB1, front contact |25 and winding of relay STO1 to Sincerelay MB1 is not up during the second on period relay STO3 is no-tpicked up.

It will be recalled that relay MF1 is up throughout the second offperiod, which is effective to close a pick-up circuit for relay STO2which extends from (-i-), front contact |26 of relay MF1, back contact|21 of relay FP1, front contact |28 of relay FC1, back contact |29 ofrelay VP1, front contact H0 of relay |V1 and winding of relay STO2 toRelay STO2 closes an obvious stick circuit for itself at its frontcontact Since relay MF1 is up during the third oi period following thedropping of relay FP1, a pickup circuit is closed for relay STO1 similarto the above described circuit for STO2, but extending through frontcontacts ||2 and |29 of relays 2V1 and VP1 respectively. Relay STO'1closes an obvious stick circuit for itself at its front contact H3. Fromthe above discussion of' the operation of the storage relays it will beapparent that the choice oi each off indication effects the energizationor the de-energization of relays STO1 and STO3, while the choice of theon indications effects the energization or the deenergization of relaysSTO2 and STO1.

Repeating' the stored ind'catz'ons. -Recalling that relay LV1 at therepeater station was picked up during the third foi period and was notdropped when relays SA1 relays FP1, SB1 and SA1 respectively, upperwindand SB1 were dropped to de-energize the other relays which werestuck ing ofrelay L01, backl contact VH of relay FC1, front contact ||5of relay LV1 and back contactk ||6 of relay VP1 to Relay L01 establishesa stick circuit for itself by way of its front Contact |I'l which iseffective after the picking up of relay VP1. At its front contact HB astick circuitA is established through back contact H9 oirelay FC1 andiront contact |70 of relay SA1, which is eiective after the lock outperiod.

In'the event that there are one or more field stations connected to theprimary line circuits between the repeater station and the controloihce, then the lockv out arrangement at these field'v stations iseffective toy prevent the transmission of repeater station storedindications to the control ofce, in the event that indications are readyfor transmission at some one of these superior field locations. The lockout feature at the repeater station is eiTective to drop relay L01 inthe event that the primary indication line circuit is interrupted by asuperior eld station. This feature is eieotive during the time intervalbetween the picking up of relay FP1 and the consequent de-energizationof the upper Winding of relay L01 at back contact |63 and there-energization of this upper winding by the picldng up of relay SA1 andthe consequent closure of its front contact Illl. It will be obviousthat during this interval, if the primary indication line circuit isopen at some superior station, then relay L01 cannot be maintainedenergized and it will be dropped away before relay SA1 is picked up tocomplete its permanent stick circuit at contact |10.

'I'he picking up o1" relay L01 previously described closes the primaryindication line circuit by the closure of front contact |56 over thecircuit which was previously pointed out. Following this energization ofthe primary indication line circuit relays MB, FC and NC in thecontroloice are picked up as previously described, with the picking upof relay NC energizing the primary control line circuit to start thesystem through a second cycle of operations. The primary control linecircuit is impulsed with a series of impulses throughout this secondindication cycle and relays F, FP, rFP, SA, E, NC and the stepping relaybank all operate in the manner previously described. Relay MB is stuckup until relay EFP drops in the rst ofi period to connect the lowerwinding of relay MB in the primary indication line circuit as laterdescribed. This stick circuit extends from front contact 60 of relay SA,front contact El; of relay 2F?, front contact 65 and winding of relay MBto Since it is assumed that no controls are to be transmitted duringthis second indication cycle, a,v series of impulses are applied to theprimary control line circuit. Relay NC1 at the repeater station followsthese impulses to transmit a series of impulses over the secondarycontrol line circuit. These impulses applied to the secondary controlline circuit eiect the intermittent operation of relays F1 and FN1 asbefore but, because relay F01 is not picked up during this secondindication cycle, the operation of relay FN1 is not effective to controlthe line repeater relays because of open front contact ld. Theintermittent actuation of contact |61? of relay F1 is effective tocontrol the line repeater relays at the repeater station because ofclosed back contact |6| of relay FC1.

The line relays at the field stations, such as the' station illustratedin Fig. 3, are responsive to the impulses applied to the secondarycontrol line circuit vduring this second indication cycle but, inaccordance with the tem disclosed in the above mentioned applicationSer. No. 640,062, stepping does not take place at these stations becauseneither the station selecting relays (such as relay SO2) nor the lockout relays (such as relay L02) are picked up.

The first or conditioning impulse applied to the control line circuitactuates contact |553 of relay F1 to the left which closes a circuit forpicking up relay FP1 extending from'(-|-) contact |60 in its right handdotted position, back contact |6| of relay F01, back contact |09 ofrelay SB1 and winding of relay FP1 to A circuit in multiple with contacti633 extends through front contact |62 of relay L01. A circuit is closedfor picking up relay SA1 which extends from front contact E58 of relayFP1, conductor 200, back contact |39 of relay F01 and winding of relaySA1 to Relay 2FP1 is not picked up during this cycle because of openfront contact |15 of relay FC1, but relay SE1 is picked up over anobvious circuit including iront contact |63 of relay SA1.

The intermittent operation of relay FP1 during this second indicationcycle is effective to operate the stepping relay bank as previouslydescribed because of closed front contact |52 of relay L01. The systemtherefore steps through a cycle of operations in the manner previouslydescribed.

During this second cycle of operations, relays PB1 and PF1 at therepeater station are positioned in accordance with the positions of thestorage relays and the primary indication line circuit is impulsed inaccordance with the positions of relays PB1 and PF1 in much the samevmanner as described in connection with the impulsing of the secondaryindication line circuit in accordance with the positions of relays PB2and PFZ.

For example, with relay ST01 picked up and stuck up as previouslyexplained relay PB1 is picked up when relay FP1 picks up, by means of acircuit extending from (-l-) front contact |99 of relay ST01, backcontacts 0| and |92 of relays |V1 and ZV1 respectively, front contact43S of relay FP1, winding of relay PB1 and front contact Id of relay L01tol When relay FP1 is dropped at the end of the conditioning on periodrelay PB1 is stuck up over an obvious circuit including its frontcontact |95. This stick circuit is maintained throughout the rst offperiod so that relay PB1 when picked up is stuck up until relay FP1again picks up to open its back contact |03.

The closure of front contact |03 extends the circuitv of relay PB1 byway of back contact |62 of relay .2V1 and front contact HH of relay |V1to front contact lil@ of relay ST03, but since relay ST03 is not pickedup relay PB1 will not be energized at this time. It drops because bothits pick-up and stick circuits are open. When relay PB1'is not picked upduring an on period it remains down throughout the following 01T period.The above illustrates how the off indications stored by relays ST01 andST03 are effective to position relay PB1.

Recalling that relay ST02 was picked up and stuck up, the dropping ofrelay W1 at the beginning of the iirst off period closes a circuit forpicking up relay PF1 which extends from front contact l'lof1elayST02,backcontact |98 of relay 2V1,front contact 220 ofrelayVP1,back contact 22| of relay FP1, Winding of relay PF1 andoperation of the sys-` front contact lili of relay L01 to With relay PF1picked up it is stuck up when relay FP1 picks up at the end of the firstolf period over an obvious circuit including front contact 22! of relayFP1 and front contact 222 of relay PF1.

The dropping of relay FP1 at the end of the first on period de-energizesthe above described stick circuit for relay PF1, but since relay STO*1is picked up relay PF1 is immediately energized over a circuit extendingfrom front contact 223 of relay STO1, front contact 224 of relay W1,back contact 22E! of relay VP1, back contact 22! of relay FP1, windingof relay PF1 and front contact lili! of relay L01 to Relay PF1 is againstuck up when relay FP1 is picked up at the beginning of the second onperiod. The above illustrates how relay PF1 is picked up during an oifperiod and maintained picked up throughout the following on period forone choice indication. It is believed obvious that the other choiceindication is effected by relays STO2 orV S'IO1 being down to effect thede-energization of relay PF1 when relay FP1 is dropped so that relay PF1will be down throughout the following on period.

Relay PB1 is picked up during the conditioning on period in preparationfor the iirst off indication as one which shall close the primaryindication line circuit, but this line circuit is not closed by PB1until Vthe following off period. When relays NC, FP and 2FP are droppedin the control ofce to apply energy to the primary indication linecircuit by way of back contacts 91, gli and S2 respectively, the primaryindication line circuit is completed because of closed front contactlli? of relay PB1 at the repeater station.

When relay NC in the control oflice picks up and opens its back Contact91 at the beginning of the first on period, the primary indication lineis de-energized and the circuit including the primary indication` lineis switched from relay MB to relay MF by way of front contacts 93 and 92of relays FP and 2FP respectively, when'these relays are picked upduring the first on period. Since reiay PF1 is up for the transmission.of an impulse over the primary indication line circuit during the firston period, the closure of iront contact 225 of relay FP1 completes theenergizing circuit for the primary indication line circuit by way ofiront Contact II'l of relay PF1. Then when relay NC drops and opens itsfront contact S5 at the beginning of the second off period the primaryindication line circuit is de-energized.

Since relay PB1 is left down in preparation for a non-pulse of theprimary indication line circuit for the second olii period, the droppingof relays FP and 2FP in the control oiilce are ineffective to close theprimary indication line circuit with back contact el oi" relay NC closedbecause of open front contact liS of relay PB1.

Since relay PF1 is up in preparation for a pulse for the second onindication of the primary indication line circuit the picking up ofrelays NC, FP and 2FP the control office completes the primaryindication line circuit because of closed front contact il? of relayPF1.

From the above it will be observed how the primary indication linecircuit is pulsed or not pulsed to provide a choice of two offindications in accordance with the position or relay PB1 at each stepand how this indication line circuit is pulsed or not pulsed to providea choice of two on indications in accordance with the position of relayPF1 at each step.

This conditioning ci the primary indication line circuit eiects theenergization and the de-energization of the MB and MF relays in thecontrol oflice in exactly the same manner as described in connectionwith the impulsing of the secondary indication line circuit forenergizing and de-ener gizing relays MB1 and VMF1 at the repeaterstation. Furthermore, this conditioning of the primary indication linecircuit transmits codes to the control cnice where they are received bythe MB and MF relays and stored on indication receiving relays in thesame manner as described in the above mentioned application Ser. No.640,-

O62. It is therefore believed unnecessary to point out in detail how,the positioning of the MB and MF relays in the office is eifective totransfer the received codesto indication storing relays.

It will be pointed out however how the MB and MF relays, when picked upin the oif and on periods respectively, are stuck up throughout thefollowing on and off periods respectively.

When relay MB is picked up during the first off period as abovedescribed, a stick circuit is closed for this relay which extends from(+L front contact 6!) of relay SA, back Contact 63 of relay E (relay Ebeing dropped before the indication line circuit is de-energized) frontcontact 65 and upper winding of relay MB to Since relay 2FP is picked upduring the first on period before relay E is picked up, a substitutestick circuit is closed by way of front contact 64 of relay ZFP which ise'ective to maintain relay MB stuck up until the following olf period,when its energization is determined by the closed condition of theprimary indication line circuit for the second off indication.

With relay MF picked up in the first on period as above described, astick circuit is closed for this relay which extends from front contact6B of relay SA, front contact 63 of relay E, front contact 66 and upperwinding of relay MF to This circuit is completed through front contact63 of relay E because relay E is picked up before they primaryindication line circuit is opened to de-energize the lower winding ofrelay MIF. Since relay 2FP is dropped before relay E opens its frontcontact 63, a substitute stick circuit is closed for relay MF whichextends through back contact Si of relay 2FP. When relay 2FP picks upduring the second on period the stick circuit of relay MF isde-energized and relay MF is dependent upon the energization of theprimary indication line circuit for the energization of its lowerwinding.

It is believed that the above examples relating to the stick circuitsfor the MB and MF relays when picked up during the first off and firston periods respectively are suicient to indicate how these relays arestuck up when picked up during other off and on periods.

At the end of the second indication cycle, during which the storedindications are transmitted to the control ofce, the last o period ofthe control line circuits is effective to de-energize the SA and SBrelays in the control oice and at the repeater station in the samemanner as previously described. The stepping relays are deenergized aspreviously described and the storage relays at the repeater station aredsa-energized when relay SB drops and opens rits front Contact 039,since at this time relay LV1 will have been dropped to open its frontcontact H4. Relay LV1 is cie-energized during the Second 011 Period bythe opening of back contact 226 of relay V131. It Will be obvious thatback contact |48 of 'transmitting contacts at the outlying field stationand at the repeater station respectively. With this arrangement ithappens that the sequence of events is such that the distributedcapacity of the .indication line circuits may become discharged .so thatthe application of energy to these circuits may result in atemporarysurge of current which is conveniently termed the chargingcurrent. This charging current flows irrespective of `whether the linecircuit is open or closed at the location from which an indication is tobe received.

It has been found in some instances that the charging current that owsinto an open circuited indication line reaches a peak value which isconsiderably greater than the current that normally flows under thestable conductive condition of the line circuit and that this chargingcurrent surge lasts for an appreciable length of time. Under theseconditions the Ymessage receiving relay in the indication line circuit,for the purpose of detecting the conductive condition of the line, maybe undesirably picked up by the charging current when such relay wassupposed to remain down in accordance with the open circuit condiltionof the line.

vIt will be recalled that the primary indication rline circuit was notimpulsed during the rst indication cycle above described because of openfront contact |56 of relay L01 of Fig. 2C. Durl ing this cycle thecontact arrangement comprising contacts 92, 93 and Sil of relays EFP andFP of Fig. 1B apply a charge to the primary indication line circuit ateach period of the cycle, which is effective to prevent the falseenergization of relay MB or MF due -to the capacity of the primaryindication line circuit. Of course the primary indication line circuitis maintained open through out this rst cycle so that one charge wouldbe suiicient. However during the second cycle a repeated charge isrequired because the primary indication line circuit may be repeatedlydischarged by a closed contact at a eid location.

YDuring the iirst indication cycle however, the secondary indicationline circuit connecting the repeater station with the distant eldstation is impulsed and the contact arrangement, comprising contacts|41, |31 and mi of relays 2FP1 and FP1 of Fig. 2C, is effective toprecharge the secondary indication line circuit.

During the transfer from one period to another, that is from an onperiod to an 01T period or viceversa, there is an interval of timeduring which the secondary indication line circuit is not energized fromindication battery IB1 and during which time the distributed capacity ofthe secondary indication line circuit may become discharged by reason ofthe closed condition of one of its controlling contacts at the eldstation.

This is because the eld station apparatus is not Y permitted to changethe condition of the secondary indication line circuit until after thisline circuit is opened at the repeater station, which is necessary toprovide that the message receiving relays MF1 and MB1 will be properlycontrolled. Thereafter, the transfer at the eld station occurs so thatupon the closure of the secondary indication line circuit at therepeater station, the conductive circuit then established is dependentupon the governing contact at the eld station. Thus it is obvious that acharging current will iiow at the beginning of each period which followsa period during which the secondary indication line circuit has beenconductively closed at the eld station, or at the beginning of a periodfollowing an interval during which the line may have been discharged forany other reason. The same discussion applies to the operation of relaysMF and MB in the oice, with energy applied to the primary indicationline circuit from battery IB.

During an on period for example, relays FP1 and 2FP1 at the repeaterstation are picked up. The relay MF1 is energized or not depending uponthe closed or open condition of contact 299 of relay PF2 at the eldstation. It will'be assumed that contact 299 of relay PF2 is closedduring the first on period. Therefore relay MF1 will be picked up, butjust before it is connected into the secondary indication line circuitthis line circuit is precharged.

When relay N01 picks up to mark the beginning of the first on period inthe control linel relay 2FP1, the indication battery is connected to thesecondary indication line circuit through charging resistor CRS1 over acircuit extending from the terminal of battery IB1, resistor CRS1, frontcontact |42 of relay FP1, back contact MI of relay 2FP1, front contactItl of relay SA1, front contact |53 of relay SB1 and back contact H59 ofrelay LV1 to secondary indication line conductor IL1. This connection ofbattery IB1 to the secondary indication line circuit through resistorCRS1 is effective to apply a charging current to the secondaryindication line circuit before the Winding of relay MF1 is inserted vinthis line circuit to detect its closed or open condition at thetransmitting eld station.

Thefirst on codeV in the secondary indication line circuit in the abovedescription was one during which the secondary indication line circuitwas closed because relay PF2 was picked up during the first off period,due to the connection to by way of jumper 282. Therefore, since thetransmission of the rst on indication is one which requires the closedcondition of the secondary indication line circuit, it will be obviousthat it was not necessary to precharge the indication circuit, becausethe message relay MF1 was supposed to pick up during this on period.However in the event that an on indication is transmitted which requiresthat this line circuit be open at the transmitting eld station, theapplication of the charging current to the line circuit just before themessage receiving relay is inserted into this line circuit charges thesecondary indication line circuit to terminate any flow of current whichmight be effective to falsely operate the message receiving relay whenit is inserted into the circuit and supposed to remain down because ofthe open condition of the indication circuit.

A similar condition exists during the transmission of off indications,for example the sec-

